Device for controlling the capacity of reciprocating compressor

ABSTRACT

A device for controlling the capacity of reciprocating compressor contains a compressor casing with a cylinder head and a cylinder disposed in said casing and provided with discharge and suction valves. The suction valve is controlled by an electromagnetic coil arranged on the exterior of the compressor casing with the electromagnetic coil being connected to the suction valve by a flux guide.

United States Patent [191 Bykov et al.

1 DEVICE FOR CONTROLLING THE CAPACITY OF RECHROCATING COMPRESSOR Filed:Dec. 29, 1972 Appl. No.: 319,399

US. Cl. 417/559, 417/505 Int. Cl. F04b 39/08 Field of Search 417/505,295, 559, 505 U, 417/295 B, 295 A, 295 T, 295 E; 91/275;25l/65;'335/237; 310/23, 24

References Cited UNITED STATES PATENTS 2,245,053 6/1941 Sanders 417/286Aug. 13, 1974 Best 251/ Hartwell et a1.. 417/505 Dunn 335/237 Pettit eta1. 310/24 Harper 335/281 Hassa 251/65 Wintriss 251/65 Freeman 251/65Duris 310/23 Primary Examiner-William L. Freeh Assistant Examiner-C. P.LaPointe Attorney, Agent, or Firm-Holman & Stern ABSTRACT A device forcontrolling the capacity of reciprocating compressor contains acompressor casing with a cylinder head and a cylinder disposed in saidcasing and provided with discharge and suction valves. The suction valveis controlled by an electromagnetic coil arranged on the exterior of thecompressor casing with the electromagnetic coil being connected to thesuction valve by a flux guide.

4 Claims, 2 Drawing Figures DEVICE FOR CONTROLLING THE CAPACITY OFRECWROCATING COMPRESSOR The present invention relates to compressorengineering, and more specifically to means for controlling the capacityof reciprocating compressors.

The invention may be used to advantage in reciprocating refrigeratingcompressors intended to handle a variety of gases including aggressiveand explosive gases such as freons, ammonia, propane and others.

PRIOR ART Known in the art are devices for controlling the capacity ofreciprocating compressors. Said device, commonly termed a compressorunloader, consists of a compressor casing with a cylinder disposedtherein. The compressor is provided with a discharge valve and a suctionvalve. The disc of the suction, valve has the shape of a ring and isunseated mechanically by means of a push rod actuated by the oilpressure build up with the aid of a pump provided on the compressor. Toreduce the output of the compressor, the cylinder is unloaded bybypassing the gas from the cylinder bore into the suction chamber of thecompressor while the disc remains unseated.

Inherent inthis arrangement is a number of disadvantages. By relying ona hydraulic power element for unseating the suction valve disc, thesystem operates with a time lag. Furthermore, breakdowns of suctionvalve discs due to the presence of the push rods actuating such discsare not uncommon. This impairs the reliability not only of thecompressor unloading system but that of the compressor and refrigeratingplant as a whole.

In addition, the above arrangement with its unloader power element and anetwork of hydraulic lines complicates the design of the compressor.

Yet, there are reciprocating compressor unloaders exerting their actionon the suction valves of the compressor directly, without recourse topush rods. For operation, these unloaders rely on an electromagneticdrive. Such unloader consists of a compressor casing with a cylinder.The upper end of the cylinder is closed by a cylinder head comprising alower plate member and an upper cover member separated by sealinggaskets. Disposed in an annular recess of the lower plate member is acoil of an electromagnet. The unloader is provided with a suction, valveand a discharge valve. The disc of the suction valve has the shape of aring. Disposed over the ring with respect to the refrigerant gas flowingfrom the suction chamber of the compressor there is a return springwhich causes the suction valve disc to seat in the valve seat to closethe suction ports. As soon as the coil is energized, the disc of thesuction valve becomes unseated and the cylinder is unloaded due to theflow of the gas from the cylinder bore into the suction chamber of thecompressor.

This arrangement has an edge over the unloader incorporating a hydraulicdrive but is also not free from a number of disadvantages. Thus, a checkup of the coil or its replacement-in the event of a failure entails adisassembly of the compressor. This calls for shutting down thecompressor, sucking off the refrigerant gas and disturbing thegas-tightness of the refrigerating plant. The gaskets serving to sealoff the coil firstly reduce the magnetizing force of electromagnet and,secondly, are likely to admit, if defective, the refrigerant gas to thecoil so that deterioration of the winding is not excluded let alone thehazard of an explosion due to arcing in the winding.

Finally, this arrangement is a power-consuming one. It is knownv thatthe magnetizing force of an electromagnet varies directly with thecurrent flowing through the winding and the number of turns in thewinding, i.e., F iw, where i is the current and w is the number ofturns. Consequently, this arrangement either draws a strong currentbringing about. heating of the coil which impairs the reliability of theunloading system or must be provided with a bulky winding adding to theoverall dimensions and weight of thecompressor.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention toeliminate said disadvantages. The principle object of the invention isto provide a device for controlling the capacity of a reciprocatingcompressor in which the coil of the electromagnet is arranged so thatthe compressor can be used in a refrigeration plant intended to handleaggressive and explosive refrigerants.

In the accomplishment of the above object, in the device for controllingthe capacity of reciprocating compressor which incorporates a coil of anelectromagnet, to control the suction valve of the compressor, said coilis arranged, according to the invention, on the exterior of thecompressor casing and is connected to the suction valve through a fluxguide.

When the coil of the electromagnet is energized, the flux so producedflows through the flux guide, with the circuit being completed throughthe suction valve body. The magnetizing force coming into play causesthe suction valve to move away from its seat.

The arrangement of the coil of the electromagnet on the exterior of thecompressor protects its winding from the corrosive effect of therefrigerant, eliminates the hazard of explosion when aggressive orexplosive gases are used and improves the cooling of the winding by thesurrounding air.

For the sake of simplicity of design, it is desirable to embody thedevice so that the flux guide is formed by the compressor casing,cylinder and discharge valve body. The flux path is through thecompressor components made from magnetic material. This plan makes anadditional flux guide superfluous, simplifies the process ofmanufacturing and the design of the device.

To add to the field strength, it is preferred to provide the flux guidewith pole tips in the form of two annular projections. These projectionsserve to concentrate the magnetic lines offorce, thereby boosting themagnetizing force. As a result, the effectiveness of the magnet isincreased whereas,the current in the coil and coil dimensions aredecreased.

It is also preferred to add a permanent magnet to the coil of theelectromagnet so that the polarity of the field produced by the formercoincides with that of the latter.

As is known, a permanent magnet produces a permanent magnetic field. Theprovision of an additional, permanent flux adding up with the flux ofthe coil of the electromagnet allows to reduce the current and thenumber of turns in the coil required to produce a magnetizing forcecapable of unseating the suction valve disc. The use of a permanentmagnet cuts power requirements, eliminates excessive heating andimproves justable shunt which short-circuits a part of the flux outsidethe suction valve disc. As the permanent magnet deteriorates with age,its magnetizing effect is increased by means of the shunt.

Other features and advantages of the present invention will be bestunderstood from the following description of a preferred embodiment whenread in conjunction with the accompanying drawings in which BRIEFDESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the device forcontrolling the capacity of reciprocating compressor according to theinvention; and

FIG. 2 is a schematic diagram of the device for controlling the capacityof reciprocating compressor according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS The device for controlling thecapacity of reciprocating compressor includes a compressor casing 1(FIGS. 1 and 2) provided with a cylinder head 2. Disposed in the casingl is a cylinder 3 with a suction valve 4 and a discharge valve 5. Thesuction valve 4 includes a ringshaped disc 6 and arranged above thering-shaped disc 6 with respect to the refrigerant flowing into thecompressor from a suction chamber (not shown) are return springs 7. Thering-shaped disc 6 is arranged to close inlet ports 8 communicating withthe suction chamber (not shown) of the compressor. The cylinder head 2has an annular recess 9. A coil 10 is connected to the suction valve 4by means of a flux guide. The flux guide is defined by the compressorcasing l, the cylinder 3 and a body 12 of the discharge valve 5, all ofwhich components are made from magnetic materials. The use of thecompressor components in the capacity of a flux guide simplifies thedesign of the device for controlling the capacity of a refrigeratingreciprocating compressor. The portion of the body 12 of the dischargevalve 5 which overlies the disc 6 of the suction valve 4 with respect tothe refrigerant flowing from the suction chamber of the compressor isprovided with pole tips in the form of two annular projections 13.Serving to concentrate the magnetic lines of force, these annularprojections 13 intensify the effective force of the electromagnet.

To produce a directional magnetic field, the annular projections 13 areseparated by a non-conductive bushing 14. A non-conductive ring 15 has asimilar function. Accommodated inside of the coil 10 is a ring-shapedpermanent magnet 16. This magnet is made so that its field has apolarity coinciding with that of the magnetic field produced by the coil10. The presence of the field produced by the permanent magnet 16 is afactor which considerably reduces the power requirements for theelectromagnetic coil 10. The permanent magnet 16 is provided with ashunt 17 in the form of a screw. By turning the screw up or down, an airgap 18 can be changed so as to control the field strength of thepermanent magnet 16 over a wide range.

The device operates as follows.

For reducing the capcity the compressor, the winding of the coil 10 isenergized, thus producing an electromagnetic field whose lines of forceare indicated in FIG. 2 by the letter a. Adding up with the field of thepermanent magnet 16 whose lines of force are indicated in FIG. 2 by theletter b, the resulting flux is passed through the flux guide defined bythe compressor casing 1, cylinder 3 and the body 12 (FIG. 1) of thedischarge valve 5 until the magnetic circuit is completed through thedisc 6 of thesuction valve 4. The magnetizing force coming into playcauses the disc 6 of the suction valve 4 to unseat against the action ofthe return springs 7. The ring-shaped disc 6 abuts against the annularprojections 13 enabling the gas to pass from the bore of the cylinder 3into the suction chamber (not shown) of the compressor through the inletports 8 and in the opposite direction. The cylinder is thus unloaded andthe output of the compressor reduced.

The device for controlling the capacity of reciprocating compressoraccording to the invention envisages the use of electromagnetic meansfor unseating the suction valves of the compressor. It can be used toadvantage in refrigeration systems employing various refrigerants,including aggressive and explosive refrigerants. The device has a simplelayout, displays exceptionally good power characteristics and low powerrequirements. Operating practically without a time lag, it can be usedin conjunction with various control systems so as to provide forpractically stepless control of the compressor output over the rangefrom full-load to no-load.

By way of illustration, the use of the invention on reciprocatingcompressors with a piston diameter of 1 15 mm and a piston stroke of 82mm has allowed a reduction in the power requirements for electromagneticvalve from 50 to 2 W.

The device has paved the way to unification of the capacity controlsystem for use with various refrigerants. A refrigerating plant equippedwith the device according to the invention is capable of controlling thevariable, say temperature, accurately to within i0.5C or even better.

What is claimed is:

1. A device for controlling the capacity of a reciprocating compressorcomprising a compressor casing, a cylinder head for said compressor, acylinder disposed in said compressor casing, a discharge valve disposedin said cylinder and a suction valve disposed in said cylinder, whereinthe improvement comprises:

an electromagnetic coil being disposed on the exterior of saidcompressor casing for controlling said suction valve; and

a magnetic flux guide being defined by said compressor casing, saidcylinder and the housing of said. discharge valve, said flux guideoperably connecting said electromagnetic coil to said suction valve.

2. The device as claimed in claim 1 in which said flux guide is providedwith pole tips in the form of two annular projections for concentratingthe magnetic lines of force. v

3. The device as claimed in claim 1 in which said electromagnetic coilis provided. with a permanent magnet producinga magnetic field whosepolarity is thelsame as that of the magnetic field produced by the cor4. The device as claimed in claim 3 in which said permanent magnet isprovided with a shunt for stabilizing the magnetic field of saidpermanent magnet.

1. A device for controlling the capacity of a reciprocating compressorcomprising a compressor casing, a cylinder head for said compressor, acylinder disposed in said compressor casing, a discharge valve disposedin said cylinder and a suction valve disposed in said cylinder, whereinthe improvement comprises: an electromagnetic coil being disposed on theexterior of said compressor casing for controlling said suction valve;and a magnetic flux guide being defined by said compressor casing, saidcylinder and the housing of said discharge valve, said flux guideoperably connecting said electromagnetic coil to said suction valve. 2.The device as claimed in claim 1 in which said flux guide is providedwith pole tips in the form of two annular projections for concentratingthe magnetic lines of force.
 3. The device as claimed in claim 1 inwhich said electromagnetic coil is provided with a permanent magnetproducing a magnetic field whose polarity is the same as that of themagnetic field produced by the coil.
 4. The device as claimed in claim 3in which said permanent magnet is provided with a shunt for stabilizingthe magnetic field of said permanent magnet.